The present invention relates to a photolithography, and more particularly, to a backside phase grating mask and a method for manufacturing the same.
As a method of increasing an integration degree of a semiconductor device, there has been suggested a method of converting a cell structure of a semiconductor device, such as a Dynamic Random Access Memory (DRAM) device, from 8F2 cell layout into 6F2 cell layout. In the 6F2 cell layout, an active region extends in a direction diagonal with respect to a word line and a bit line, which are perpendicular to each other, thereby allowing arrangement of more transistors within a limited area. A pattern delimiting the active region is a diagonal pattern which is rotated by a predetermined angle with respect to the word line or the bit line.
The diagonal pattern is introduced, unlike the word line or the bit line, not in the form of a rectangular coordinate system but in the form extending in a direction rotated by a predetermined angle on the rectangular coordinate system. Thus, a modified illuminating system which is adapted to the rectangular coordinate system cannot be effective on the diagonal pattern. The modified illuminating system such as a dipole illuminating system, though introduced to improve a resolution limitation of an exposure light source, can obtain a desirable effect when a transferred pattern is a line and space pattern which extends in an X-axis direction or a Y-axis direction of an XY rectangular coordinate system.
The modified illuminating system, such as an X-axis dipole having a pair of dipoles arranged in an X-axis, improves the resolution of line and space patterns extending in a Y-axis direction. However, when the X-axis dipole illuminating system is employed in an exposure process of pattern-transferring diagonal patterns rotated by a predetermined angle with respect to a Y-axis, a position angle of the dipole and a position angle of an edge of the diagonal patterns are deviated from each other. Thus, the effect of improving resolution by dipole illumination can be reduced by half. Moreover, a pattern defect results because the diagonal patterns cannot be pattern-transferred in the form extending along a designed direction, but its extending direction is deviatedly moved toward the Y-axis direction by the dipole illumination. That is to say, the diagonal pattern transferred onto a wafer can be transferred not with a designed rotation angle with respect to the Y-axis but with a smaller angle.
Therefore, it is required to develop an improved illuminating system.